Cross-linking cellulosics with epichlorohydrin vapors



United States Patent US. Cl. 8--120 9 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to a novel process for the rapid wetcross-linking of cellulosic materials to impart wet configurationalmemory thereto, more particularly to the strong base catalyzedcross-linking of cellulosic materials in a continuous manner with hotepichlorohydrin vapors.

In US. Patent No. 2,985,501 there is disclosed a method of wetcross-linking cellulosic fabrics with epichlorohydrin while the fabricis impregnated with moisture and strong base catalyst. The reaction rateof this method is such that several hours is usually required to obtaincomplete reaction at room temperature. As would be expected, thisreaction time can be reduced by heating the fabric while impregnatedwith the moisture, strong base and epichlorohydrin. However, because ofthe volatility of the epichlorohydrin, this method of accelerating thereaction is not practical in a batch-wise process above about 60 C.Also, in a batch-wise process, above about 90 C. the efficiency of thereaction apparently is reversed and the desired cross-linking reactiondoes not proceed properly so that much less fiat drying properties areimparted to the cellulosic material. Thus, the cross-linking ofcellulosic materials with epichlorohydrin has heretofore had to beconducted in a time consuming batch-wise procedure requiring from aboutone-half hour to several hours for completion of the reaction.

It was surprising therefore to find that, when following the process ofthis invention, the desired cross-linking reaction proceeds efiicientlyand very rapidly at temperatures substantially above those which resultin a poor reaction under the prior batch-wise procedures.

Another surprising effect observed when following the process of thisinvention is that the strength loss inherent in cross-linking ofcellulosic materials is less for any given degree of flat dryperformance than is obtained when the cross-linking reaction is achievedby applying liquid epichlorohydrin to the cellulosic material in abatchwise manner.

It is therefore an object of this invention to provide a rapid methodfor cross-linking cellulosic materials with epichlorohydrin while thematerial is impregnated with moisture and strong base to impart wetresiliency thereto.

Another object is to provide a continuous process for cross-linkingcellulosic,- preferably cotton, fabric with epichlorohydrin.

Still another object is to provide a method of reducing the strengthloss obtained when cross-linking cellulosic materials withepichlorohydrin to impart Wet configurational memory thereto.

Other objects will be apparent to those skilled in the art to which thisinvention pertains.

According to this invention, a cellulosic material uniformly impregnatedwith up to 130% moisture and at least about 1% strong base catalystcalculated as NaOH, both calculated on the weight of the dry cellulosicmaterial, is cross-linked at a rapid rate with epichlorohydrin bycontacting the material with hot epichlorohydrin vapors 3,506,391Patented Apr. 14, 1970 until between about 1% and 7%, calculated on theweight of the dry cellulosic material and as NaOH, of strong base hasbeen consumed.

In the preferred form of this invention, cellulosic material in webform, preferably woven fabric, which is uniformly impregnated with up tomoisture and 15% strong base catalyst is passed continuously in theselected configuration into contact with hot epichlorohydrin vaporsuntil substantially all of the catalyst has been consumed and is thenheated at a temperature above about the boiling point of epichlorohydrinuntil substantially all of the epichlorohydrin is removed from thematerial.

The term wet configurational memory as used herein means that thecellulosic material treated according to the present process tends toreturn, after being distorted or crumpled while in the wet state, to theconfiguration in which it was in when the cross-linking reaction tookplace. In the case of yarn, this means that the yarns can be compactedwhile wet and if they were cross-linked in an uncrumpled state, theyarns will tend to straighten themselves if permitted to do so. Fabricsknitted or woven from such treated yarns will also resist wrinklingwhile being washed. If the yarn is cross-linked in a crumpled position,the resulting yarn and fabric prepared therefrom will have a bulkedeffect and will resist being distorted into a smooth configuration. Whenfabrics are treated in a smooth, wrinkle-free state, the cross-linkedfabric will thereafter resist wrinkling in the wet state. These fabricscan therefore be washed and spin-dried in an automatic washer or wrungout by hand and will dry on the line substantially wrinkle-free.

Cellulosic materials which can be cross-linked according to the processof this invention are those which are normally cross-linked to impartwet configurational memory thereto, e.g., natural and regeneratedcellulose, and cellulose derivatives having only a portion of the freecellulosic hydroxy groups esterified or etherified so that at least 1.8free hydroxy groups per anhydroglucose unit remain, e.g.,lower-hydrocarbon esters, including the acetate, propionate, butyrate,benzoate and sulfate, phosphate, and aryl and alkyl sulfate esters, andlower-alkyl ethers, including methyl, and ethyl, and hydroxyalkyl,including hydroxyethyl, and carboxymethyl and carboxyethyl ethers, andthe other known cellulose esters and ethers. The natural cellulosicmaterials can be in the form of cotton, linen, jute, flax, and thesynthetic cellulosic materials can be in the form of filament or stapleviscose, both unmodified and modified, e.g., the polynosic rayons. Thecellulosic material can also have had a prior textile resin treatment,e.g., with urea-formaldehyde, melamineformaldehyde, cyclic ethyleneurea, dihydroxy cyclic ethylene urea, triazone, or other commonlyemployed textile resin, so that the material already has substantial dryconfigurational memory and, to a lesser degree, wet configurationalmemory.

The novel process is directed primarily and preferably to cellulosicmaterials in web form, including knitted, non-woven and woven fabrics,but the advantages of this invention can also be achieved by treatingthe cellulosic fibers, yarns or threads employed to produce these webs.The preferred cellulosic material is cotton fabric which is preferablywoven, e.g., printcloth, broadcloth and sheeting. Although the processwill ordinarily be conducted on cellulosic material consisting entirelyof cotton or rayon, the process is equally applicable to such yarns andfabrics also containing synthetic filaments or fibers, e.g., theglycol-terephthalate polyesters, nylon, and the polyacrylics. Preferablythe cellulosic material comprises at least 40% or more by weight of thematerial to be treated and more desirably about 60% or more.

The strong base catalysts for the cross-linking reaction 3 include thealkali-metal hydroxides, e.g., sodium hydroxide and potassium hydroxide,the quaternary ammonium hydroxides, e.g., trimethylphenyl ammoniumhydroxide, and alkali-metal salts which, in the presence of moisture,produce a strongly alkaline solution, e.g., the alkali-metal sulfidesand alkali-metal silicates. When the Salts are employed, they should beemployed in amount which will impart an alkalinity to the solution inabout the samerange as that obtained when an alkali-metal hydroxide isemployed. Because the cellulosic material tends to lose strengthproportionally to the amount of strong base catalyst present thereinduring the reaction, the amount of catalyst present initially on thematerial desirably is less than 10%, calculated stoichiometrically asNaOH and on the weight of the dry fabric, preferably between 1% and 7%and more preferably between about 1% and 5%, e.g., between about 2.0%and 4%. The optimum amount of catalyst which should be present in thefabric under any given set of conditions will depend in part upon themanner in which the strong base is applied, the total moisture presentduring the reaction and the total reaction time.

. For example, if the catalyst is applied as a relatively dilute, e.g.,2-5%, aqueous solution by padding so that the material is completelywetted out, the amount present on the fabric is ideally between about 2and 4%. If the catalyst is applied as a relatively concentrated aqueoussolution, e.g., 10-50%, in limited amounts, e.g., byrneans of a printroll, the amount applied is ideally between from 0.75 to 2. If betweenabout 1% and 5% is applied, the reaction can be continued untilsubstantially all of the strong base is consumed.

As stated above, the cross-linking reaction is conducted while thecellulosic material is impregnated, initially at least, with moisture asWell as the strong base catalyst. Moisture is most conveniently providedby applying the strong base catalyst to the fabric in the form of anaqueous solution. The amount of moisture present during the reaction,while not critical within a fairly wide range in producing wetconfigurational memory in the material, can affect the amount of dryconfigurational memory imparted to the cellulosic material. For example,if the total moisture present in the material exceeds about 15%,calculated on the dry weight of the material, wet configurational memoryis imparted to the material but little if any significant dryconfigurational memory. On the other hand, when the total moisturecontent is below about 15%, good wet and dry configurational memory canbe imparted to the material. The minimum amount of moisture which shouldbe present to ensure adequate crosslinking is very low, i.e., in therange of 0.5-2%, which is considerably lower than the moisture contentof cotton at normal atmospheric humidities. The maximum moisture whichshould be present to ensure adequate crosslinking is about 130%, but ispreferably below about 100%, and most preferably below about 85%,calculated on the dry Weight of the fabric. If the moisture level of thecellulosic material after being impregnated with strong base catalyst istoo high, an intermediate drying step can be introduced to reduce thetotal moisture level, e.g., to 3-15 Pre-heating of the material can alsobe employed to reduceexcessive cooling in the reaction chamber andexcessive condensation of liquid epichlorohydrin on the fabric.

As stated above, the moisture and strong base can be applied by padding,applicator roll, print roll, spraying, etc. so long as it is uniformlydistributed throughout the material in a manner which will avoidundesired distortion of the material, e.g., crinkling and puckering,etc. If the strong base is deliberately applied unevenly, a plisseeffect can be produced in fabrics or a wool-like effect with fibers.Ordinarily, it is desired to apply the strong base uniformity to fabric,e.g., by immersing in an excess of an aqueous solution of the selectedstrong base and squeezing through nip rolls to remove the excess baseand moisture, as flat drying properties are imparted to fabric underthese conditions.

The selected material is then passed into a closed system for contactingwith epichlorohydrin. The term closed system means that the system issealed against extraneous leakage of epichlorohydrin vapors. Obviously,an entrance and exit for the cellulosic material must be provided butleakage of vapors can be avoided by vapor seals. Also, an outlet abovethe condensation system must also be provided, but significant amountsof epichlorohydrin will not escape if the condensation system isadequate. The cellulosic material should be in the desired configurationwhile being in contact with the epichlorohydrin and impregnated with thestrong base catalyst. Ordinarily, this will mean, e.g., that fabric ispassed open width into the chamber and maintained in a smooth,wrinkle-free condition during the reaction period.

A dwell period must be provided for contacting the material withepichlorohydrin vapors for a time sufiicient to consume between about 1%and 7%, calculated as NaOH and on the weight of the dry cellulosicmaterial, of strong base catalyst, e.g., 5 seconds to 10 minutes,preferably 30 to 300 seconds. This can be achieved with a Bentelerbatcher system or a festoon system, if the material is in web form, orby a series of rolls or aprons if the material is in yarn or untwistedfiber form.

The epichlorohydrin can be contacted with the cellulosic material invapor form by providing a sump-type arrangement heated, e.g., with steamcoils, to maintain a reservoir of liquid epichlorohydrin at its boilingpoint, and passing the cellulosic material above the surface of theboiling epichlorohydrin. The material should not be passed into contactwith the surface of the boiling epichlorohydrin as this adverselyaffects the process. I

The gaseous epichlorohydrin rapidly reacts with the cellulosic materialWhile at the same time consuming the strong base catalyst and removingsome or all of the water in the material. Means preferably should beprovided to remove this water from the system to prevent a build-up ofit therein, e.g., by a condenser system with a trap arrangement wherebythe water is separated from the epichlorohydrin as both are condensed.As the epichloro hydrin consumes the strong base catalyst While reactingwith the cellulosic material, the reaction is self-terminating ifsuflicient reaction time is provided. Thus, it is not necessary to avoidcontacting the material with an amount of gaseous epichlorohydrinconsiderably in excess of the theoretical amount required and, in fact,it is desirable to do so. It is preferred that the material be contactedwith an amount of gaseous epichlorohydrin at least equivalent in molesto the amount of strong base present on the material, but lesser orgreater amounts can be employed, if desired, e.g., from 0.5 to 20%,calculated on the weight of the dry cellulosic material.

When the cross-linking reaction has proceeded to the desired extent oris complete, the cellulosic material will be saturated with impregnatedexcess epichlorohydrin, particularly if the fabric has not beenmaintained at a temperature at or above the boiling point ofepichlorohydrin. To improve the economics of the process and to avoidhandling the material impregnated with epichlorohydrin in the open, itis preferably thereafter heated, e.g., with steam heated dry cans or byradiant means to a temperature above the boiling point ofepichlorohydrin. To prevent recondensation of the epichlorohydrin in thematerial, this heating step is preferably conducted above thecondensation height of the epichlorohydrin in the closed chamber, e.g.,by maintaining the heating means above the level where theepichlorohydrin vapors are condensed by the cooling system, or conductedin a separate portion of the closed chamber which is maintained at atemperature above the boiling point of epichlorohydrin.

The textile material can thereafter be washed in the usual fashion, ifdesired, to remove any traces of reactants or reaction by-products.

The following examples are illustrativeof the process of this invention.

EXAMPLE 1 Bleached and mercerized 3.19 yd./lb. at 40" 136 x 64 cottonbroadcloth having filling tensile strength of about 62 lbs. is passedopen width continuously into a pad box containing 3.5% aqueous NaOH,then through squeeze rolls to provide an 80% pick-up thereof, and thenthrough vapor seals into a closed chamber. The chamber is equipped nearits top with a water cooled condenser having a Starke-Dean trap whichreturns the condensed epichlorohydrin to the bottom of the chamber andremoves water from the system. The bottom of the chamber has steam coilswhich heat the liquid epichlorohydrin to its boiling point. A floatdevice attached to a source of epichlorohydrin maintains a constantvolume of epichlorohydrin in the system. Above the condensation level ofthe epichlorohydrin are dry cans steam heated to above the boiling pointof epichlorohydrin. Below the condensation level of the epichlorohydrinis provided a festoon system for moving the fabric open width and in aWrinkle-free condition. The NaOH impregnated fabric is passedcontinuously through the festoon system at a speed that provides a 120second exposure time to the epichlorohydrin vapors. The fabric is thenpassed over the dry cans so that substantially all of theepichlorohydrin is removed from the fabric, which is then removed fromthe closed chamber through a vapor seal and into washing tanks. Theresulting fabric has a Wet crease recovery angle of at least 140,filling tensile of at least 30 lbs. and will rate at least 4.0 by thestandard flat drying test involving passing a square of the fabricthrough the spin cycle of an automatic washer containing a standard loadto damp dry the fabric and then line drying the fabric and thencomparing the degree of wrinkling of the fabric with standard plasticsamples under low angle single source lighting conditions.

Any or all of the following variations can be introduced into theabove-described system:

(1) The concentration of the NaOH can be varied between about 0.75% and15%, e.g., 1%, 2%, 3%, 4% or 5%, depending on the degree of flat dryingdesired and the amount of residual strength to be retained.

(2) Pick-up of the NaOH solution can be varied between about 35% and100%, e.g., 40%, 50%, 60%, 70%, 90% or 100%.

(3) The exposure time can be varied between about 30 seconds and 300seconds withthe shorter exposure times preferably being employed inconjunction with higher NaOH concentrations.

(4) The heating of the fabric on the dry cans to remove residualepichlorohydrin can be omitted or replaced by radiant heating.

(5 KOH can be substituted for the NaOH.

(6) In all of the above-described reaction conditions, the dwell timecan be adjusted to consume all or any desired portion of the strong basecatalyst.

EXAMPLE 2 Samples of 180 count percale sheeting containing varyingamounts of aqueous sodium hydroxide, obtained by immersing the fabric ina caustic solution of the selected concentration and blotting to apick-up of about 80- l00%, are exposed in a closed system to the vaporsfrom boiling epichlorohydrin for various periods of time, washedthoroughly and then tested for wet crease recovery. Results obtainedfrom such experiments are shown in Table I below.

1 Fabric then heated at about 117 C. to drive off all epichlorohydrincondensed on fabric before washing.

EXAMPLE 3 The procedure of Example 2 is followed on 4.00

yd./lb. bleached and mercerized 80 x 80 printcloth. The results of suchexperiments are shown in Table II below.

TABLE II Wet crease NaOH recovery Strip tensile concentra- Exposureangle (filling) Sample tlon, percent time (see) (filling)(deg.) (lbs.)

Control 2. 5 0 92 39. 5 1 2. 5 so 116 33.8 2. 5 120 144 23. 3 10 60 14525. 0 10 120 156 22.0 15 144 31. 8

What is claimed is:

1. A process for the rapid cross-linking of hydrated cellulosicmaterials with strong base catalyzed epichlorohydrin to impart wetconfigurational memory thereto which comprises the steps of continuouslypassing the material, impregnated with up to 130% moisture and betweenabout 1% and 7% of strong base catalyst calculated as NaOH, bothcalculated on the weight of the dry cellulosic material, into a closedsystem containing liquid epichlorohydrin heated to its boiling point;contacting the material in a selected configuration in the closed systemwith gaseous epichlorohydrin in an amount in excess of that required tocompletely consume the base catalyst; and maintaining the material incontact with the epichlorohydrin vapors in the selected configuration inthe closed system for at least five seconds until between about 1% and7%, calculated as NaOH and on the Weight of the dry cellulosic material,of strong base catalyst has been consumed.

2. A process according to claim 1 wherein the strong base catalyst is analkali-metal hydroxide.

3. A process according to claim 1 wherein the cellulosic material iscotton fabric.

4. A process according to claim 1 wherein the starting cellulosicmaterial is impregnated with at least about 5% moisture and betweenabout 1% and 5% alkali-metal hydroxide.

5. A continuous process for the rapid cross-linking of hydrated cottonfabric with alkali-metal hydroxide catalyzed epichlorohydrin whichcomprises the steps of continuously passing the fabric, uniformlyimpregnated with up to about moisture and between about 1% and 5%alkali-metal hydroxide, calculated on the Weight of the dry fabric, intoa closed system containing liquid epichlorohydrin heated to its boilingpoint; contacting the fabric in the closed system while in a smoothwrinkle-free condition with the vapors produced by boilingepichlorohydrin present in the closed system in an amount in excess ofthat required to completely consume the base catalyst; and contactingthe fabric in a smooth, wrinkle-free condition with the epichlorohydrinvapors in the closed system for at least about 30 seconds untilsubstantially all of the alkali-metal hydroxide has been consumed.

6. Process according to claim 5 wherein the fabric contains betweenabout 2% and 4% alkali-metal hydroxide.

7. Process according to claim 5 including the additional step ofheating'the fabric above about the boiling point of epichlorohydrinbefore removal from the closed chamber.

8. A continuous process for wet cross-linking cotton fabric to impartwet resiliency thereto which comprises the steps of padding the fabricwith an aqueous alkalimetal hydroxide solution with a pick-up thereof ofbetween about 35% and 100%, the concentration of the alkali-metalhydroxide solution being such as to provide the fabric with betweenabout 2% and 4% alkali-metal hydroxide at the selected pick-up,calculated on the weight of the dry fabric; passing the thus-impregnatedfabric into a closed system, provided with condensing means andcontaining liquid epichlorohydrin heated to its boiling point;contacting the fabric while in the closed system in a smooth,Wrinkle-free condition to the vapors of boiling epichlorohydrin in anamount in excess of that required to completely consume all of the basecatalyst for at least about 30 seconds until substantially all thealkalimetal hydroxide has been consumed; and heating the fabric while inthe closed system above about the boiling point of epichlorohydrin whileout of contact with said vapors of epichlorohydrin to volatilizeresidual epichlorohydrin from the fabric; and concomitantly recoveringthe volatilized epichlorohydrin.

9. A process of modifying cellulosic materials which comprises the stepsof continuously passing the material, impregnated with a catalyticamount of a strong base catalyst and at the desired moisture level, intoa closed system containing liquid epichlorohydrin heated to its boilingpoint, contacting the material in the closed system with gaseousepichlorohydrin and maintaining the material in contact with theepichlorohydrin vapors for a sufficient period of time to eifectimprovement in said materials crease recovery properties.

References Cited UNITED STATES PATENTS 1,863,208 6/1932 Schorger 81201,741,637 12/1929 Lilienfeld 8120 2,985,501 5/1961 Gagarine 812O2,109,295 2/1938 Lawrie 8120 2,202,169 5/1940 Schlack 8133 2,823,6145/1958 Kersnar 8120 FOREIGN PATENTS 696,282 10/ 1949 Great Britain.

478,259 5/ 1937 Great Britain.

724,096 10/ 1952 Great Britain.

518,225 7/1939 Great Britain.

467,992 6/ 1937 Great Britain.

489,940 8/ 1938 Great Britain.

DONALD LEVY, Primar Examiner I. CANNON, Assistant Examiner US. Cl. X.R.8115.7, 129

